In this study, the effect of black cumin oil in different concentrations (1%, 1.5% and 2%) was examined on the microbiological quality of rainbow trout (Oncorhynchus mykiss) fillets. The study groups were separated in four as control group (A) without containing cumin black oil, group (B) containing 1% black cumin oil, group (C) containing 1.5% black cumin oil, and group (D) containing 2% black cumin oil